Reduced engine operation times in hybrid vehicles enable fuel economy and reduced fuel emissions benefits. However, the shorter engine operation times can lead to insufficient time for completion of various on-board diagnostic operations. These may include, for example, diagnostics for various engine exhaust sensors, exhaust catalyst monitoring, etc.
One example approach to enable completion of on-board diagnostic routines involves maintaining or resuming engine operation for a duration to complete the routines. Another example approach is shown by Matsuoka et al. in U.S. Pat. No. 6,446,61 wherein an engine is held in a steady-state during engine operation so that a diagnostic routine can run.
The inventors herein have recognized issues with such approaches. For example, starting an engine or maintaining an engine at steady state to perform diagnostic routines may be intrusive to vehicle operation and may negatively impact customer perception of engine run time in a hybrid vehicle. Further, fuel efficiency may be reduced in approaches which indiscriminately start or extend engine run time in order to complete diagnostic tests while the hybrid vehicle is in operation.
Further, it may be desirable to perform deceleration fuel shut off (DFSO), where fuel supply is discontinued to the engine, in order to expose a sensor or catalyst to greater extremes of air/fuel mixtures in order to ensure high-confidence failure code settings when diagnosing faults in exhaust system components, such as air/fuel sensors and catalysts. Due to the minimal engine running time for hybrid vehicles, e.g., such vehicles may be configured to shut the engine down in response to driver tip-outs, exhaust sensors in the exhaust system may not be adequately exposed to rich and lean air/fuel mixtures needed for monitoring.
In one example, some of the above issues may be addressed by a method for operating a hybrid vehicle comprising inhibiting engine shutdown and enabling deceleration fuel shut off to perform a monitoring test while a vehicle speed is above a threshold speed.
In this way, diagnostic routines may be performed using DFSO to adequately expose exhaust sensors to rich and lean air/fuel mixtures in order to more accurately diagnose exhaust system components while reducing intrusiveness of the monitoring routines on vehicle operation. Further, in such an approach, fuel economy may be increased by inhibiting engine pull-downs only when the diagnostic monitor is ready. Further, by not causing the engine to stay on below threshold speeds, customer satisfaction with hybrid vehicle operation may increase. For example, the monitor will not intrude into the noticeable low-speed area of vehicle operation, even with a suspect sensor.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.